The knitting proved slightly more difficult. Had I been working on a flat surface it would not have been a problem but this was a sweater and the pattern had to wrap round the body and meet up. No matter how I tried I could not get it to match exactly. Sometimes, when things look as though they really should work, it is hard to grasp the reason why they just won’t.

Fortunately, Ben was on hand and spotted the problem instantly. “It’s irrational”, was his comment. At first I took this as a comment on my state of mind but then realised he was talking about irrational numbers.

Root 2 is one of those numbers with a long string of numbers after the decimal point that never ends. There is no exact answer. Knitting is very forgiving and the small discrepancies are taken up by slight stretching. The calculations would never work out but the knitting would look good enough to pretend they did.

I knitted a lilac and white version, then an evening version in black with sparkly black shapes between (It does not photograph well). The third version was to be a long tunic with huge flowers, made from squares and rhombuses. It was impossible to arrange the flowers so they flowed correctly from back to front so we worked on the assumption that nobody could look at the back and front simultaneously, and that wearer would need to have their arms in the air for the cheating to be revealed. So far no one has ever mentioned that some flowers are missing a petal.

At a Mathematics Conference, the speaker at the opening session showed a black and white pattern and said, “Turn to the person next to you and say something about this pattern”. Steve was sitting on one side so I turned to the complete stranger sitting on the other side and said, “I could knit that!” Poor man. His face showed all that he was thinking!

The pattern was made from the type of shapes we had been working with. Of course I could knit it and I could find seven different ways to colour it in such a way that it was difficult to believe they were all versions of the same pattern. (Other effects can be seen if the design is used in the original orientation.) The colouring was easy and I sent the coloured versions to the speaker from that opening session. I believe he included them in an academic paper he was writing at the time.